The opening match in the Pete Sampras Group produced a feast of stylish backhands from both players but it was Dimitrov, the first Bulgarian to qualify for the tournament in its 48-year-old history, who overcome some late jitters to prevail.

World number six Dimitrov served for the match at 5-4 in the decider but was broken to love before two consecutive double faults by Thiem gave him another chance to close it out.

Again Dimitrov wobbled, squandering two match points at 40-15 with a double-fault and a forehand error, but he finally bagged the win when Thiem looped a backhand long.

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“The first time I got broken (at 5-4) I thought ‘okay let’s get back up and try again’,” Dimitrov, who enjoyed some noisy support from a contingent of Bulgarian fans, said on court.

“I’m living my dream right now and I wanna keep on going.”

World number one Rafael Nadal opens his quest for a first ATP Finals title later against Belgium’s David Goffin.

Nadal’s appearance has been in doubt after a knee injury forced him to withdraw midway through the Paris Masters tournament.